In medical imaging, for example, in X-ray imaging or in ultrasound imaging, proper positioning of a patient before a medical examination is important for the diagnostic quality of the radiograph, which therefore may require exhaustive education and training. Positioning error is one of the main reasons that cause the examinations to be repeated, which may cause not only extra costs but also additional e.g. X-ray exposure for the patient. For example, WO 2013/072814 A1 describes the positioning of an X-ray source relative to a patient.